The transcription factor hepatic leukemia factor (HLF) is strongly expressed in hematopoietic stem cells (HSCs) and is thought to influence both HSC self-renewal and leukemogenesis. However, the physiological role of HLF in hematopoiesis and HSC function is unclear. Here, we report that mice lacking Hlf are viable with essentially normal hematopoietic parameters, including an intact HSC pool during steady-state hematopoiesis. In contrast, when challenged through transplantation, Hlf-deficient HSCs showed an impaired ability to reconstitute hematopoiesis and became gradually exhausted upon serial transplantation. Transcriptional profiling of Hlf-deficient HSCs revealed changes associated with enhanced cellular activation, and cell-cycle analysis demonstrated a significant reduction of quiescent HSCs. Accordingly, toxic insults targeting dividing cells completely eradicated the HSC pool in Hlf-deficient mice. In summary, our findings point to HLF as a critical regulator of HSC quiescence and as an essential factor for maintaining the HSC pool during regeneration.

Culture conditions in which hematopoietic stem cells (HSCs) can be expanded for clinical benefit are highly sought after. Here, we report that inhibition of the epigenetic regulator lysine-specific histone demethylase 1A (LSD1) induces a rapid expansion of human cord blood–derived CD34+ cells and promotes in vitro propagation of long-term repopulating HSCs by preventing differentiation. The phenotype and molecular characteristics of cells treated with LSD1 inhibitors were highly similar to cells treated with UM171, an agent promoting expansion of HSCs through undefined mechanisms and currently being tested in clinical trials. Strikingly, we found that LSD1, as well as other members of the LSD1-containing chromatin remodeling complex CoREST, is rapidly polyubiquitinated and degraded upon UM171 treatment. CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 depletion of the CoREST core member, RCOR1, resulted in expansion of CD34+ cells similar to LSD1 inhibition and UM171. Taken together, LSD1 and CoREST restrict HSC expansion and are principal targets of UM171, forming a mechanistic basis for the HSC-promoting activity of UM171.

Significance: Primary stem cells are difficult to transfect, and their viability and function are impaired by traditional transfection methods. We show that nanostraws can be used to deliver RNA to primary human hematopoietic stem cells without any detectable negative effects. Nanostraw-treated cells show no alterations in gene expression and fully retain their proliferative capacity and their potential to regenerate blood cells of different lineages in vivo. This nonperturbative transfection method can benefit functional studies and clinical applications where minimal impact on stem cell function and viability is required.

Identification of determinants of fate choices in hematopoietic stem cells (HSCs) is essential to improve the clinical use of HSCs and to enhance our understanding of the biology of normal and malignant hematopoiesis. Here, we show that high-mobility group AT hook 2 (HMGA2), a nonhistone chromosomal-binding protein, is highly and preferentially expressed in HSCs and in the most immature progenitor cell subset of fetal, neonatal, and adult human hematopoiesis. Knockdown of HMGA2 by short hairpin RNA impaired the long-term hematopoietic reconstitution of cord blood (CB)–derived CB CD34+ cells. Conversely, overexpression of HMGA2 in CB CD34+ cells led to overall enhanced reconstitution in serial transplantation assays accompanied by a skewing toward the myeloerythroid lineages. RNA-sequencing analysis showed that enforced HMGA2 expression in CD34+ cells induced gene-expression signatures associated with differentiation toward megakaryocyte-erythroid and myeloid lineages, as well as signatures associated with growth and survival, which at the protein level were coupled with strong activation of AKT. Taken together, our findings demonstrate a key role of HMGA2 in regulation of both proliferation and differentiation of human HSPCs.

Chronic myeloid leukemia (CML) is maintained by leukemic stem cells (LSCs) which are resistant to the existing TKI therapy. Hence a better understanding of the CML LSCs is necessary to eradicate these cells and achieve complete cure. Using the miRNA-gene interaction networks from the CML lin(−) cells we identified a set of up/down-regulated miRNAs and corresponding target genes. Association studies (Pearson correlation) from the miRNA and gene expression data showed that miR-1469 and miR-1972 have significantly higher number of target genes, 75 and 50 respectively. We observed that miR-1972 induces G2-M cell cycle arrest and miR-1469 moderately arrested G1 cell cycle when overexpressed in KCL22 cells. We have earlier shown that a combination of imatinib and JAK inhibitor I can significantly bring down the proliferation of CML lineage negative cells. Here we observed that imatinib and JAK inhibitor I combination restored the expression pattern of the down-regulated miRNAs in primary CML lin(−) cells. Thus effective manipulation of the deregulated miRNAs can restore the miRNA-mRNA networks that can efficiently inhibit CML stem and progenitor cells and alleviate the disease.